1. Field of the Invention
This invention relates to an improvement in a fluid coking process. More particularly, this invention relates to a fluid coking process in which hydrogen sulfide is added to the fluidizing gas.
2. Description of the Prior Art
Fluid coking is a well known process which may be carried out with or without recycle of the heavier portion of the fluid coking zone effluent. As is well known in the art, the fluid coking process, shown, for example, in U.S. Pat. No. 2,881,130, which is hereby incorporated by reference, uses a fluid coking vessel and external heating vessel. A fluid bed of solids, preferably coke particles produced by the process having a size in the range from about 40 to about 1000 microns is maintained in the coking zone by the upward passage of fluidizing gas, usually steam, injected at a superficial velocity usually between 0.3 and 5 feet per second. The temperature in the fluid coking bed is maintained in the range of from about 850.degree. to about 1200.degree. F., preferably between 900.degree. and 1100.degree. F. by circulating solids (coke) to the heating vessel and back. The heavy oil to be converted is injected into the fluid bed and upon contact with the hot solids undergoes pyrolysis evolving lighter hydrocarbon products in vapor phase, including normally liquid hydrocarbons, and depositing a carbonaceous residue (coke) on the solids. The turbulence of the fluid bed normally results in substantially isothermal reaction conditions and thorough and rapid distribution of the heavy injected oil. Product vapors, after removal of entrained solids, are withdrawn overhead from the coking zone and sent to a scrubber and fractionator for cooling and separation. The end boiling point of the distillate fraction obtained from the process is usually 1,050.degree. to 1,200.degree. F. and the remaining heavy ends are usually recycled to extinction.
U.S. Pat. No. 3,848,017 discloses thermal cracking of vaporized normally liquid hydrocarbons comprisng added hydrogen sulfide.
U.S. Pat. No. 3,853,744 discloses the use of sour steam containing minor amounts of hydrogen sulfide as fluidizing gas for a fluid coking bed.
U.S. Pat. Nos. 2,888,395 and 2,888,393 disclose fluid coking with added hydrogen.
It is also known to utilize light hydrocarbons to supplement or be used as fluidizing gas in fluid coking as shown in U.S. Pat. Nos. 2,636,844; 2,734,852 and 2,863,823.
It has now been found that the addition of a relatively large amount of hydrogen sulfide to the fluidizing gas of the coker will result in advantages that will become apparent in the ensuing description.